Israeli Prime Minister Benjamin Netanyahu said on Tuesday that Hezbollah movement had dug cross-border tunnels from Lebanon to insert militants into northern Israel.

Netanyahu said Israel took the decision to act against the tunnels "weeks ago" and moved into action on Tuesday morning. He said the operation would continue as long as necessary and was a "small part" of a deployment on all fronts to "defend Israel."

Israel's military said on Tuesday it had begun an operation to "expose and thwart" cross-border attack tunnels from Lebanon dug by the Iran-backed Lebanese movement Hezbollah.

Israeli military spokesman Lt Col Jonathan Conricus said the military had detected tunnels crossing from Lebanon into northern Israel. He said the Israeli operation to counter the tunnels would be inside Israel, and would not cross the border.

As the operation started, Israeli journalists reported that the Israeli security cabinet plans to meet on Tuesday evening in the Israeli army headquarters in Tel Aviv to discuss the situation at the border.

Israel released video footage of digging and pile-driving equipment at work in unidentified locations, carrying out what it said were "tactical preparations to expose Hezbollah's offensive cross-border tunnel project". The footage could not be immediately verified.

The situation appeared calm on the Lebanese side of the border where UN peacekeepers and Lebanese troops were deployed as usual, a Reuters journalist there said. There was no immediate comment from Hezbollah.

Israel and Hezbollah have avoided any major conflict across the Lebanese-Israeli border since their last war in 2006, though Israel has mounted attacks in Syria targeting what it said were advanced weapon deliveries to the group.

On Monday, Israeli Prime Minister Benjamin Netanyahu met US Secretary of State Mike Pompeo in Brussels.

Netanyahu told his government's ministers in a cabinet meeting on Tuesday that he agreed with Pompeo to bring new sanctions and a UN resolution against Hezbollah.

The current focus of operations was near the Israeli border town Metulla, Conricus said, adding that some areas near the border fence had been closed off. An Israeli military source said the operation might take weeks to complete.

Netanyahu's hints

The military said the tunnels were not yet operational but posed "an imminent threat" to Israeli civilians, and constituted "a flagrant and severe violation of Israeli sovereignty".

It said the army had "enhanced its presence and readiness" and was prepared for "various scenarios".

In September, Netanyahu identified three locations in Lebanon where, he said, Hezbollah was converting "inaccurate projectiles" into precision-guided missiles.

Netanyahu last month hinted at an upcoming Israeli offensive during a televised address, saying: "I will not say this evening when we will act and how. I have a clear plan. I know what to do and when to do it. And we will do it."

He said an upcoming security challenge would require Israelis to "endure sacrifice".

Last year, Hezbollah's leader said any future conflict with Israel could take place inside Israeli territory, and there would be "no place that is out of reach of the rockets of the resistance or the boots of the resistance fighters".

Israel’s vulnerability to tunnels was laid bare during its war with Palestinian group Hamas in Gaza in 2014 when Palestinian fighters used dozens of secret passages dug from Gaza into Israel to launch surprise attacks.